How do I perform a superficial radial nerve block at the wrist, including patient positioning, anatomical landmarks, needle technique, stimulation parameters, and appropriate local anesthetic volume?

Superficial Radial Nerve Block at the Wrist

The superficial radial nerve block at the wrist is performed by infiltrating 3-5 mL of local anesthetic subcutaneously in a circumferential band from the radial styloid dorsally toward the anatomical snuffbox, targeting the nerve as it emerges between the brachioradialis and extensor carpi radialis longus tendons approximately 8-9 cm proximal to the radial styloid. 1, 2

Patient Positioning and Ergonomic Setup

• Position the patient supine with the arm abducted on an armboard, forearm in neutral to slight pronation 3
• Adjust the procedure table height to within 5 cm above to 10 cm below your elbow level to minimize neck and back flexion 3
• Place equipment trolley on your dominant side to minimize torso torsion 3
• Ensure adequate lighting and quiet environment free from distraction 3

Anatomical Landmarks and Nerve Course

The superficial branch of the radial nerve becomes subcutaneous at a mean of 9.0 cm proximal to the radial styloid, emerging between the brachioradialis and extensor carpi radialis longus tendons 2. Key anatomical considerations include:

• The nerve pierces the forearm fascia approximately 6.0 cm proximal to the radial styloid 4
• First branching occurs at a mean of 5.1 cm proximal to the radial styloid 2
• An average of 3.4 to 5.8 branches cross the wrist joint level 5, 4
• In approximately 30% of cases, a branch runs directly across the radial styloid apophysis, requiring careful technique 5
• The lateral antebrachial cutaneous nerve may extend into the thumb region in up to 47% of cases, potentially requiring supplemental blockade for complete anesthesia 6

Procedural Technique

Preparation

• Verify drug allergies and calculate maximum safe dose based on patient weight 1
• Check local anesthetic ampules for name, concentration, and expiration date 1
• Prepare injection site with antiseptic solution 7, 8
• Draw local anesthetic into a 10-mL syringe with appropriate needle 1

Injection Technique

• Identify the radial styloid and the tendons of brachioradialis and extensor carpi radialis longus 1, 2
• Insert needle subcutaneously at the radial styloid level 1
• Aspirate before injection to ensure the needle is not intravascular 7, 8
• Inject slowly over 20 seconds to minimize discomfort and tissue trauma 8
• Create a subcutaneous wheal extending dorsally from the radial styloid toward the anatomical snuffbox 1
• Infiltrate in a fan-like pattern to capture the multiple nerve branches 1, 4

Ultrasound-Guided Approach (When Available)

If using ultrasound guidance, which improves accuracy when landmarks are uncertain 9:

• Position ultrasound machine directly opposite the operator with screen at eye level 3
• Use a palmar grip on the transducer, holding it toward its base to minimize wrist torque 3
• Employ in-plane needling along the visual axis for improved accuracy 3
• Visualize local anesthetic spread in real-time around the nerve branches 9

Local Anesthetic Volume and Selection

• Use 3-5 mL of local anesthetic for adequate coverage of the superficial radial nerve distribution 1
• Amide-type local anesthetics (lidocaine, bupivacaine) are preferred over ester-type agents 8
• Warm the local anesthetic solution to room temperature or slightly above to reduce injection discomfort 8
• Allow sufficient onset time (10-15 minutes for lidocaine, 15-20 minutes for bupivacaine) before proceeding 8

Critical Safety Considerations and Common Pitfalls

Aspiration is mandatory before every injection to prevent intravascular administration, which can cause seizures, cardiovascular collapse, and respiratory arrest 7, 8. Additional safety measures include:

• Avoid intraneural injection by never injecting against high resistance 1
• Be aware that nerve stimulation is not typically used for this superficial sensory nerve block 1
• Recognize that the superficial radial nerve provides purely sensory innervation with no motor component 1
• Consider supplemental blockade of the lateral antebrachial cutaneous nerve if anesthesia of the thumb base is inadequate, as this nerve extends into the radial thumb region in approximately 47% of patients 6
• Exercise extreme caution when performing procedures near the radial styloid, as 30% of patients have a nerve branch directly crossing this landmark 5
• Maintain aseptic technique throughout the procedure 3

Expected Outcomes

The landmark technique provides effective anesthesia for the dorsoradial hand, typically covering the radial 2.5 to 3.5 digits (thumb, index finger, and radial aspect of long finger) 2, 4. The block produces no motor deficit, making it suitable when intraoperative active motion is required or when immediate postoperative physiotherapy is planned 1.